Identification of proteins in leaf tissues of white clover using MALDI-TOF mass spectrometry

Abstract

Protein extracts, made to leaves harvested from the stolons of the pasture legume white clover (Trifolium repens L.) at two developmental stages (newly initiated; onset of senescence) were purified further using reverse-phase and ionexchange chromatography. Fractions enriched with the ethylene biosynthetic enzyme 1-aminocyclopropane-1-carboxylate (ACC) oxidase were selected for each stage and the final, partially purified fraction was subjected to twodimensional gel electrophoresis (2DE). Antibodies raised against a recombinant ACC oxidase (ACO) from white clover (antiTR-ACO2) recognised a series of spots of differing pI suggesting that ACO undergoes post-translational modifications. Further, the pattern differed between the ACO proteins partially purified from newly initiated leaves with leaves at the onset of senescence suggesting that the environmental and developmental cues that operate in each tissue influences the type and/or degree of post-translational modifications of the ACO protein. MALDI-TOF mass spectrometry was used to identify protein spots associated with the ACO proteins. Protein with identities to an ACO isoform from Oryza sativa, and a phosphoribulokinase from Arabidopsis thaliana were identified in the 2DE separations from newly initiated leaves, while an isoflavone reductase from Medicago sativa was identified in the 2DE separation of the senescent leaf extract.